David Cameron has promised to intervene in the intensifying row over rebel Tory MEPs who are trying to prevent a toughening of Europe's climate targets.

At prime minister's questions, he told MPs that Downing Street enforcers would be talking to the MEPs who are threatening to revolt in a Brussels vote to raise the EU carbon cutting target from 20% to 30% of emissions by 2020. The rebellion threatens to dent the green credentials of the prime minister and the coalition.

Senior Tory ministers told the Guardian they were "in dialogue" with their colleagues in the European parliament. The energy minister, Charles Hendry, said: "It is clearly government policy to go for 30%. There has been engagement on this from No 10 and at the ministerial level."

Cameron was responding to a question from the Labour shadow energy and climate change secretary, Luciana Berger, prompted by a Guardian report that the leader of the UK Conservative grouping in the European parliament was instructing his MEPs to vote against the strengthening of the target.

The vote takes place on Thursday. It will not determine whether the EU moves to the more ambitious target, but it will be seized on by opposing European governments and factions within the European commission to support their preference.

Martin Callanan, leader of the UK Conservative MEP grouping, told the Guardian he would vote against the stiffer target because it would harm business.

He said before Cameron spoke: "I have not discussed our position with No 10. We are being consistent with our long-standing position, from long before the coalition was formed, and we are not in coalition with the Lib Dems in the European parliament. When Chris Huhne announced the coalition's support for the increase to 30% he did not consult us on the matter. If he had done so, then I would have informed him of our views. Lib Dem MEPs also often vote against coalition policy."

But this is at odds with the official Downing Street line. Cameron, who has repeatedly said this will be the "greenest government ever", has committed the UK to the steepest emissions cuts in Europe, and the coalition has thrown its weight behind the push for a 30% EU target, gathering support from several other member states.

For his MEPs to vote against the proposal would be embarrassing to the prime minister and is likely to provide ammunition to those countries which oppose raising the 2020 target. Poland, which takes over the presidency of the EU next month, is opposed to raising the target, and on Tuesday blocked a debate on the issue by European environment ministers.

Said one Brussels observer: "[Opponents of the more ambitious target] will exploit these Tory divisions."

Cameron stopped short of giving a guarantee, but said the government was still committed to the target and he would talk to his MEPs – if Berger would talk to Labour MEPs on areas where their policies diverged from the party's Westminster stance.

Berger said: "It's a sign of how far the Conservative party's green mask has slipped when the prime minister can't rely on his own MEPs to vote for a coalition policy. Britain should be a leading voice in the EU, calling for ambitious targets to tackle climate change. Instead we are resigned to the sidelines by a Conservative Party that professes to be green but doesn't act green. If the prime minister wants to lead the greenest government ever, he can't be held hostage by his own party. His green credentials will be judged on whether his MEPs vote for the 30% target tomorrow."

Chris Davies, the Lib Dem environment spokesman in the European parliament, said the vote was a "crucial test" of Tory MEPs. "Raising the target to 30% is crucial if low carbon investment is to be stimulated, and the policy of the coalition government could not be clearer.

"It's well known that there are climate change deniers in the Conservative ranks in Brussels and it seems now that they have gained the upper hand."